The Allylic Acetoxylation of 1,1-Disubstituted Alkenes Catalyzed by a Palladium(II)/Monothiadiazole Ligand System

Abstract

A palladium(II)/monothiadiazole ligand catalytic system and its application in catalyzing the acetoxylation of 1,1-disubstituted alkenes have been developed. With this newly designed monothiadiazole thioether ligand, the reaction showed a broad scope with respect to 1,1-disubstituted olefins, giving the corresponding products in yields of 30–86%.

Key words

palladium catalysis - ligands - acetoxylation - alkenes - regioselectivity - allylic oxidation

• References and Notes

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• 9 Allylic Acetates 2a–r; General Procedure To a stirred mixture of Pd(OAc)₂ (0.05 equiv), ligand L6 (0.05 equiv), Et₃N (2.0 equiv), and 1,4-benzoquinone (2.0 equiv) in AcOH (1 mL) was added the appropriate substrate (1.00 mmol) in one portion at r.t. The resultant mixture was stirred at 40 °C for 12–24 h then cooled to r.t. The reaction was quenched with sat. aq NaHSO₃, and the mixture was diluted with H₂O and CH₂Cl₂. The organic layer was separated, and the aqueous layer was extracted with CH₂Cl₂. The combined organic layers were dried (Na₂SO₄), filtered, and concentrated under reduced pressure to afford a brown oil that was purified by column chromatography (silica gel, CH₂Cl₂–hexane or EtOAc–hexane) to afford the allylic acetate as a colorless to pale-yellow oil or solid. 2-[(2R,8R,8aS)-8,8a-Dimethyl-6-oxo-1,2,3,4,6,7,8,8a-octahydronaphthalen-2-yl]prop-2-en-1-yl Acetate (2n) Prepared according to the general procedure from (+)-nootkatone (218 mg, 1.00 mmol). The crude product was purified by column chromatography [silica gel, EtOAc–hexane (1:10)] to give a white solid; yield: 168 mg (61%, 0.61 mmol). ¹H NMR (500 MHz, CDCl₃): δ = 5.75 (s, 1 H), 5.07 (s, 1 H), 4.97 (s, 1 H), 4.60–4.54 (m, 2 H), 2.50 (m, 1 H), 2.37 (m, 2 H), 2.28–2.18 (m, 2 H), 2.09 (s, 3 H), 1.99 (m, 4 H), 1.40–1.32 (m, 1 H), 1.09 (s, 3 H), 0.95 (d, J = 6.8 Hz, 3 H). ¹³C NMR (126 MHz, CDCl₃): δ = 199.3, 170.6, 169.7, 147.3, 124.8, 111.8, 66.0, 44.1, 41.9, 40.3, 39.3, 36.3, 32.9, 31.7, 20.9, 16.7, 14.8. HRMS (EI-TOF); m/z [M – C₂H₂O₂] calcd for C₁₅H₂₂O: 218.1678; found: 218.1671.
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